How important is UV protection after the procedure?

I've been looking into various options while considering getting skin care, and I've come across a lot of talk saying that post-procedure care is more important than the procedure itself. In particular, there are many posts emphasizing the importance of proper sun protection, so I'm wondering just how much attention I actually need to pay to it.

I usually apply sunscreen, but I often don't reapply it if I'm not out for a long time. However, I would like to know how often I should reapply it after laser treatments or skin care, and whether it is also advisable to use a hat or parasol.

I've also seen mentions that hyperpigmentation can occur if proper UV protection isn't maintained after the procedure, and I'm curious if anyone has actually experienced this. Since I've never had the procedure done, I'd like to learn about aftercare in advance. Please share any tips on how you usually protect yourself from UV rays.